Sensors for detecting leaks

ABSTRACT

A sensor for detecting leakage of a particular fluid into an area to be monitored, such as an interstitial space of a double-walled tank or pipeline, comprises first and second fiber optics. A first end of the first fiber optic is disposed to a source of light and a first end of the second fiber optic is disposed to a detector of light. The second ends of the fiber optics are axially aligned with one another. Under normal circumstances light is transmitted from the source to the first fiber optic across the gap into the second fiber optic, and is detected by the detector. The fiber optics are arranged such that when the sensor is exposed to a material to be monitored, effective light-transmission between the second ends of the fiber optics is prevented, preventing light from being transmitted from the source to the detector. This provides a simple and fool-proof method of detecting leakage of the fluid to be monitored into the area to be monitored.

BACKGROUND OF THE INVENTION Cross Reference to Related Applications

This application is a continuation-in-part of application Ser. No.07/720,229 filed Jun. 25, 1991 by the same inventor.

FIELD OF THE INVENTION

This invention relates to inexpensive and reliable sensors for detectingleaks that are particularly suitable for being disposed between thewalls of double-walled tanks, between inner and outer pipes ofdouble-walled piping, in soil, and for related uses.

Description of the Prior Art

The prior art includes many attempts to provide reliable detection ofleaks of the contents of tanks, pipelines and the like. Detection ofleaks in a simple, efficient and reliable fashion is highly desired atpresent because of increased public awareness of the sensitivity of theenvironment to chemical spills and the like. Moreover, increasingregulatory activity mandates reduction of industrial leakage of toxicchemicals and the like, and detection and cure of such leaks beforetheir effects can become dangerous or catastrophic.

The prior art has not provided suitable sensors for detecting leaks fromtanks, including both single and double-walled tanks, and includingtanks on ships, railcars, trucks and the like, as well as tanks buriedin or resting on the ground, and from double-walled pipelines and othervessels. In many circumstances, individual valves, pumps and fittingsmust be separately monitored, necessitating a simple and inexpensivesensor. In general, prior art leak detectors have been undulycomplicated and thus both expensive and prone to erroneous signals.Moreover, many prior art leak detectors attempt to provide quantitativemeasurement of leakage, requiring costly construction techniques,frequent calibration, complex instrumentation and the like.

The art requires a simple, low cost, fool-proof sensor providingunambiguous, objective detection of leaks.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a simple,low-cost, easily installed, readily monitored sensor for detection ofleaks, particularly suitable for monitoring the interstitial spaces ofdouble-walled tanks or pipelines and the like, and also suitable fordetecting leaks from other sources, such as pumps, valves, fittings andthe like.

It is a further object of the invention to provide a simple, fool-proofand low-cost sensor for monitoring leakage providing an objective,non-quantitative indication of whether a leak is present.

These and other objects of the invention appearing as the discussionbelow proceeds are satisfied by the present invention of a sensorcomprising a first fiber optic having a first end juxtaposed to a sourceof illumination and a second fiber optic having a first end disposed injuxtaposition to a detector of illumination. The second ends of the twofiber optics are axially aligned with one another for efficient lighttransmission therebetween. Under normal circumstances light from thesource is detected at the detector.

In a first embodiment of the sensor of the invention, the second end ofone of the fiber optics is biased to move away from the axially alignedposition, but is normally restrained from doing so by a latch membermade of a material deteriorating in the presence of a particular fluidto be monitored for leakage. For example, if gasoline is to be detecteda rubber member under tension may be employed as a latch element. Rubberloses its tensile strength when exposed to gasoline. Therefore, if sucha sensor is exposed to gasoline, the latch member deteriorates, allowingthe bias to move the second end of one of the two fiber optics out ofalignment with the other. Under these circumstances, light from thesource is not detected at the detector, indicating that the latch hasbeen destroyed by leaking gasoline. Monitoring the condition of thesensor may be performed at the location of the sensor or remotely.

In another embodiment, the tips of the two fiber optics may normally bemaintained in alignment by a tube enclosing their tips. The tube is of amaterial which swells and moves the tips out of alignment with oneanother upon exposure to the fluid being monitored for leakage.

In a further embodiment of the sensor of the invention, a continuousfiber optic may be disposed to monitor leakage in an interstitial spacein a double-walled pipeline or the like. Cutters responsive to the fluidbeing monitored are disposed at intervals along the fiber optic. Thecutters cut the fiber optic when the sensor is exposed to the fluidbeing monitored.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodimentstaken in conjunction with the accompanying drawings wherein like partsin each of the several figures are identified by the same referencecharacters.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood if reference is made to theaccompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a double-walled tank illustrating atypical installation of a leak sensor according to the invention;

FIG. 2a is a cross-sectional view of the sensor according to theinvention in a first embodiment thereof in a "normal" condition, andschematically shows the use of a source and a detector of illuminationto monitor the condition of the detector;

FIG. 2b is a view of the sensor of FIG. 2a, showing the sensor in its"leakage detected" condition;

FIG. 3a is a view corresponding to FIG. 2a of a second embodiment of thesensor of the invention;

FIG. 3b is a view of the sensor of FIG. 3a in a view corresponding toFIG. 2b;

FIG. 4a is a view corresponding to FIG. 2a illustrating a thirdembodiment of the sensor of the invention;

FIG. 4b is a view of the sensor of FIG. 4a in a view corresponding toFIG. 2b;

FIG. 5 is a partly cut away side elevational view of a pipelineincorporating a continuous fiber optic having a number of leak sensorsaccording to the invention disposed therealong;

FIG. 6a is a side elevational view of a leak sensor suitable for use inthe system of FIG. 5 in a "normal" position; and

FIG. 6b is a view of the sensor of FIG. 6a in a "leakage detected"condition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a double-walled tank 10 includes an inner tank12 within an outer tank 14. Tank 10 may be in or on the ground, asshown, or may form part of a tank ship, a railcar, or a highway truck.Tank 10 contains a fluid such as gasoline, leakage of which is to bedetected. (The term "fluid" as used herein and in the appended claims isintended to include vapors as well as liquids.) An interstitial space 16is defined between the inner tank 12 and the outer tank 14. A sensor 18according to the invention extends through the wall of the outer tank 14such that its active components extend into the interstitial space 16.As indicated the sensor 18 according to the invention is preferablydisposed at a position in the interstitial space 16 where it is likelyto detect leakage at an early stage thereof, typically at the lowestpoint.

The sensor of the invention may also be used to monitor leakage from asingle-walled tank, e.g., by disposition in a gravel-filled sump in theground near the single-walled tank, and may also be employed for fluidlevel detection. The sensor of the invention may likewise be employed tomonitor leakage from other sources, such as pumps, valves, and otherfittings. If the sensor 18 is disposed in an inaccessible position, thesensor 18 may be connected by signal leads or fiber optics to a moreconvenient monitoring location 19.

FIG. 2a shows a first embodiment of the sensor 18 according to theinvention in its "normal" condition, that is, before detection ofleakage. As used to detect leakage from the inner tank of adouble-walled tank, the sensor 18 may comprise a plug 20 extendingthrough the wall 22 of the outer tank 14. A first fiber optic 24, thatis, an optical fiber including a core and a cladding, and capable ofefficiently transferring illumination from a source 26 juxtaposed to afirst end 24a of the fiber optic 24 to a second end 24b thereof, extendsthrough the plug 20. A second fiber optic 28 also extending through plug20 has a second end 28b disposed in efficient light transmittingrelationship with the second end 24b of the first fiber optic, and afirst end 28a juxtaposed to a light detector 30, such as aphototransistor. In the "normal" condition of sensor 18, the second ends24b and 28b of the first and second fiber optics 24 and 28 respectivelyare axially aligned with one another to ensure efficient lighttransmission therebetween. In the normal condition of the sensor 18shown in FIG. 2a, light from the source 26 is transmitted along thefirst fiber optic 24, passes between second ends 24b and 28b, istransmitted along the second fiber optic 28, and is detected by thedetector 30.

As indicated schematically the condition of the sensor 18 can beconveniently monitored by a hand-held monitoring instrument 34.Instrument 34 comprises, for example, a light source 26, a battery 32for powering light source 26, a light detector 30 such as aphototransistor, an amplifier 36 for amplifying the signal provided bythe light detector 30 upon detection of illumination, and an outputindicator 38 such as an LED or the like illuminated to provide a visibleindication that light from source 26 has been detected by detector 30.The light source 26 may also be a simple flashlight, and the conditionof the sensor 18 may be monitored visually by attempting to detect lightemitted from the first end 28a of the second fiber optic.

In order to permit monitoring of the condition of the sensor 18 from aremote location, the first ends of the first and second fiber optics mayextend from an inaccessible location on tank 10 to an accessiblemonitoring location 19 to allow a worker to juxtapose an instrument 34thereto, as shown in FIG. 1. Alternatively, the sensor assembly maycomprise a light source and detector connected to a remote monitoringlocation by suitable power supply and control leads. The response of thesensor being monitored may also be recorded, as indicated at 39.Numerous other monitoring arrangements are possible.

According to the invention, the sensor 18 is constructed so that if thesensor is exposed to a fluid to be monitored the second ends 24b and 28bof the fiber optics 24 and 28 are no longer in their original efficientlight-transmitting relation to one another. In typical embodiments ofthe sensor of the invention, exposure thereof to the fluid to bemonitored will simply cause the mating ends 24b and 28b of the fiberoptics 24 and 28 to move with respect to one another, effectivelydestroying the normal efficient light-transmitting relation. Hence asubsequent monitoring step carried out using instrument 34 (orotherwise, as noted) will indicate that a leak has occurred.

Use of the sensor of the invention to monitor tanks and other vesselsfor leakage simply requires that the condition of the sensor beperiodically monitored, as above. It will be appreciated that thecondition of the sensor may be monitored simply by determining whetherlight is transmitted from the source to the detector; no accuratemeasurement of the light transmissivity of the sensor need be made, forexample.

In the embodiment of the sensor 18 of the invention shown in FIG. 2a and2b, the second ends 24b and 28b of the fiber optics 24 and 28 arenormally maintained in axial alignment by a band 40 of a materialaffected by the fluid being monitored, allowing one of the second endsto move out of axial alignment with the other. For example, if leakageof gasoline or another hydrocarbon is to be monitored, the band 40 maybe made of a natural rubber losing its tensile strength when exposed togasoline. The second end 24b of the first fiber optic 24 is biased tomove out of axial alignment with the second end 28b of the second fiberoptic 28 when the band 40 deteriorates upon exposure to the fluid to bemeasured. A bend 24c formed in the first fiber optic 24 upon manufacturemay be sufficiently acute to provide adequate bias; alternatively, aseparate biasing spring 42 may be provided to ensure that the end 24b ofthe first fiber optic 24 moves out of axial alignment with the end 28bof the second fiber optic 28 upon deterioration of the band 40 byexposure to gasoline.

When the sensor 18 is exposed to gasoline, the sensor 18 assumes the"leak detected" condition shown in FIG. 2b, wherein the band 40 hasruptured responsive to the bias exerted thereon by the bend 24c in thefirst fiber optic 24, and the second end 24b of the first fiber optic 24has moved out of alignment with the second end 28b of the second fiberoptic 28. Thereafter, if the instrument 34 is juxtaposed to the firstends 24a and 28a of the fiber optics, no illumination from source 26will be detected by detector 30.

In lieu of the band 40, a mass of material soluble in the fluid to bemonitored, such as tar in the case of a sensor intended to monitor theleakage of gasoline, may be employed to maintain the alignment of thesecond ends 24b and 28b against bias provided by a bend 24c and/or aspring 42. Alternatively, a mass of a material that swells when exposedto the fluid to be monitored, such as certain so-called "RTV" (i.e.room-temperature-vulcanizing) silicone rubber compounds sold forsealing, caulking, and like uses, may be disposed so as to positivelyurge the second end 24b of the fiber optic 24 out of efficientlight-transmitting relation with the mating end 28b of the second fiberoptic 28. Certain RTV silicone materials have the property of returningto their original configuration when dried after exposure to the fluidthat causes their expansion; this property is useful in manufacturing asensor according to the invention for liquid level detection or thelike.

FIG. 3a shows a second embodiment of the sensor of the invention in itsnormal condition, while FIG. 3b shows the same sensor 18a in its "leakdetected" condition. Again the sensor 18a comprises a plug 20, a firstfiber optic 24 having a first end 24a adapted to be juxtaposed to asource of illumination carried by a monitoring instrument 34 (as in FIG.2a), and again the first fiber optic 24 includes a second end 24bjuxtaposed to a second end 28b of a second fiber optic 28. Fiber optic28 also again includes a first end 28a adapted to be juxtaposed to adetector 34 for monitoring the condition of the probe 18a. However, inthis case the second ends 24b and 28b are normally maintained in axialalignment with one another by a tube 46 of a material affected byexposure to the fluid to be monitored so that exposure to the fluid tobe monitored destroys the efficient light-transmitting relation of thesecond ends 24b and 28b of the fiber optics 24 and 28. If the fluid tobe monitored is gasoline, the tube 46 may be made of a natural rubber.When such a tube 46 is exposed to gasoline, it swells; thereupon, asshown in FIG. 3b, the ends 24b and 28b move out of efficientlight-transmitting relation with one another. Illumination from a sourcejuxtaposed to the first end 24a of the first fiber optic 24 is then noteffectively communicated to the second fiber optic 28. This "leakdetected" condition may be detected by an instrument 34 as shown in FIG.2a, or otherwise, as indicated above. The selection of the material ofthe tube with respect to the fluid to be detected may also be such thatwhen the tube is exposed to the fluid to be detected, it will contract,bringing the ends of the fiber optics more closely together andincreasing the efficiency of transmission of light therebetween.

The selectivity of the probe 18a may be increased by encapsulating thetube 46 in a layer 48 of a material which is selectively porous to orsoluble in a particular material to be monitored. For example, it mightbe desirable for mechanical reasons to use a tube 46 of a materialexpanding upon exposure to either gasoline and water. Such a probe 18awould indicate that a leak had occurred upon exposure to either water orgasoline. To eliminate this ambiguity, the tube 46 may be encapsulatedin a layer of a material 48, such as wax or tar, that is porous to orsoluble in gasoline but resistant to water. Encapsulating the tube 46will typically also slow deterioration of the material of tub 46 due tothe passage of time.

In a further embodiment of the sensor of the invention shown in FIGS. 4aand 4b, the sensor 18b again comprises a plug 20 through which a firstfiber optic 24 and a second fiber optic 28 extend, so that a first end24a of a first fiber optic 24 may be juxtaposed to an optical sourcecomprised by a monitoring instrument 34 (as in FIG. 2a) and a first end28b of the second fiber optic can similarly be juxtaposed to a detectorcomprised by an instrument 34. A second end 24b of the first fiber optic24 is juxtaposed to a second end 28b of the second fiber optic 28.

However, in the embodiment of the sensor 18b of the invention shown inFIGS. 4a and 4b, the ends 24b and 28b of the fiber optics 24 and 28 donot move with respect to one another upon exposure of the sensor 18b toa particular fluid to be monitored. Instead, the efficiency oftransmission of light between the axially aligned ends 24b and 28bvaries upon exposure of the sensor 18b to the fluid to be monitored. Forexample, many fiber optics are formed of plastic materials the surfacesof which are pitted by vapors of materials of interest, such asgasoline. Accordingly, if such fiber optics were used, it would bepossible to monitor leakage of gasoline vapors by monitoring the lighttransmission of the sensor 18b over time, that is, by maintaining thesecond ends 24b and 28b of the fiber optics in a fixed relation to oneanother, periodically juxtaposing a source of consistent intensity tothe first end 24a of the first fiber optic, measuring the illuminationlevel detected at the first end 28b of the second fiber optic 28,storing the result employing recorder 39 (FIG. 2a), and comparing theresult to previously stored results. A change would indicate that thelight-transmitting qualities of the surfaces of the ends of one or bothof the fiber optics 24 and 28 had deteriorated due to exposure togasoline vapor.

In a further improvement, a member 50 of a material which is translucentor transparent in its normal state and opaque due to pitting or crazingafter exposure to vapors of the fluid to be monitored may be disposedbetween the ends 24b and 28b of the fiber optics 24 and 28. For example,a thin sheet, e.g. 0.001 inch thick, of the plastic sold under thetrademark "Lexan" by General Electric Company is normally transparent,but becomes substantially opaque when exposed to gasoline. Thus, if nolight is detected at a first end 28b of second fiber 28 uponjuxtaposition of a light source to first end 24b of first fiber 24, aleak may be taken to have been detected. Alternatively, the amount oflight detected at a first end 28a of the second fiber optic 28 inresponse to juxtaposition of a source of consistent intensity to thefirst end 24a of the first fiber optic 24 may be monitored over time,e.g. employing recorder 39 (FIG. 2a), and any change taken to indicatethat the sensor 18 b has been exposed to vapor.

As discussed in connection with the embodiment of the inventiondescribed in connection with FIGS. 3a and 3b, the selectivity of thesensor 18b may be improved if necessary by encapsulating the matingsecond ends 24b and 28b of the fiber optics 24 and 28 in a material 52which is selectively porous to or soluble in the particular fluid beingmonitored.

It will be appreciated by those of skill in the art that gaps betweenmating sections of fiber optics, as discussed in connection with thesensors of the invention discussed in connection with FIGS. 2a-4b, willoccasion some attenuation of the illumination at each gap. Accordingly,sensors having gaps between adjacent fiber optic sections are bestsuited for applications wherein a limited number of sensors is adequateto measure the leakage in a particular space, such as the interstitialspace of a tank assembly 10 shown in FIG. 1. If a large number of suchsensors 18 were disposed in series, for example to monitor the conditionat a like number of points in the interstitial space between the innerand outer pipes in a double-walled pipeline system, the totalattenuation might be too great to provide reliable detection. Accordingto another aspect of the invention, a continuous fiber optic may bedisposed in the interstitial space between inner and outer pipes of adouble-walled piping system and be positively cut if a leak occurs,providing an unambiguous indication of a leak into the interstitialspace.

FIG. 5 shows a pipeline comprising an inner pipe 60 resting on supports62 in an outer pipe 64. A continuous fiber optic 66 is disposed in theinterstitial space 69 to detect leakage of liquid, and has a number ofidentical sensors 68 discussed in connection with FIGS. 6a and 6bdisposed therealong. A second similar assembly of a continuous fiberoptic and a number of sensors (not shown) may be disposed in the upperportion of the interstitial space 69 to monitor vapor leakage ifdesired.

A suitable sensor 68 is shown in its normal condition in FIG. 6a and inits "leak detected" condition in FIG. 6b. The sensor 68 comprises a pairof pincer arms 70 and 72 pivoted with respect to one another at a pivot74. The pincer arms 70 and 72 are biased by a spring 80 to bring opposedjaws 76 and 78 together. The fiber optic 66 is disposed between cuttingedges of the jaws 76 and 78. In the normal condition shown in FIG. 6a,the spring 80 is restrained from bringing the jaws 76 and 78 together bya latch member 82. Latch member 82 is affected by the fluid to bemonitored so as to release the pincer members 70 and 72. In theembodiment shown the latch member 82 may comprise a band of materialthat loses its tensile strength when exposed to the fluid to bemonitored, allowing the jaws 76 and 78 to sever the fiber optic 66.Alternatively, a mass of material soluble in the fluid to be monitoredmay be disposed between the ends of pincer members, adjacent to the jaws76 and 78. When the sensor is exposed to the fluid to be monitored, andthe mass of material dissolves, spring 80 will force the pincer membersto pivot with respect to one another about the pivot member 74, bringingthe jaws 76 and 78 together, and severing the cable 66. In a furtherembodiment, the spring 80 and latch 82 may both be supplanted by a massof material that expands when exposed to the fluid of interest disposedbetween the ends of pincer arms 70 and 72 opposite the jaws 76 and 78.When this mass of material is exposed to the fluid to be monitored, itwill swell, forcing the jaws 76 and 78 together, severing the fiberoptic.

In each of these embodiments, monitoring of the condition of the fiberoptic may be accomplished by disposing a source of illumination at oneend of the fiber optic 66 and a detector at the opposite end. Thismonitoring step can be carried out periodically by two workmen workingas a team at either end of the cable or remotely from a central controllocation, or otherwise.

Having described preferred and alternative embodiments of new andimproved sensors for detecting leaks, and more generally for detectingthe presence of particular fluids at the sensor locations, it isbelieved that other modifications, variations and changes will besuggested to those skilled in the art in view of the teachings set forthherein. It is therefore to be understood that all such variations,modifications and changes are believed to fall within the scope of thepresent invention as defined by the appended claims.

What is claimed is:
 1. A sensor for detecting the presence of aparticular fluid, comprising:a first fiber optic having a first endadapted to be juxtaposed to a source of illumination and a second end; asecond fiber optic having a first end adapted to be juxtaposed to adetector of illumination and a second end; said second end of saidsecond fiber optic being disposed in a particular efficientlight-transmitting relationship with said second end of said first fiberoptic in the absence of said particular fluid; and means for moving saidsecond ends of said first and second fiber optics with respect to oneanother so as to alter said particular efficient light-transmittingrelationship responsive to the presence of the particular fluid.
 2. Thesensor of claim 1, wherein said particular efficient light-transmittingrelationship of said second ends of said fiber optics is closejuxtaposition of said second ends of said fiber optics in axialalignment with one another.
 3. The sensor of claim 1, wherein said meansfor moving includes means for biasing said second ends of said first andsecond fiber optics out of said particular efficient light-transmittingrelationship with one another and said sensor further comprises meansfor maintaining said second ends of said first and second fiber opticsin said efficient light-transmitting relationship with one another. 4.The sensor of claim 3, wherein said means for maintaining comprisesmeans deteriorating in the presence of the particular fluid, wherebysaid second ends of said fiber optics are moved by said biasing meansout of said particular efficient light-transmitting relationship.
 5. Thesensor of claim 4, wherein said deteriorating means includes a rubbermember maintained under tension against said bias, and the particularfluid is a hydrocarbon liquid or vapor.
 6. The sensor of claim 4,wherein said bias is provided at least in part by spring means adaptedto separate said second ends upon deterioration of said means formaintaining responsive to the presence of said particular fluid.
 7. Thesensor of claim 4, wherein one of said fiber optics is curved to take arelatively sharp bend, whereby said bias is provided by the tendency ofsaid fiber to straighten.
 8. The sensor of claim 3, wherein said meansfor maintaining said second ends of said first and second fiber opticsin efficient light-transmitting relationship with one another comprisesa member adapted to receive and retain said second ends of said firstand second fiber optics, said member being formed of a materialdeteriorating upon exposure to said particular fluid.
 9. The sensor ofclaim 8, wherein said member adapted to receive said second ends is atube for receiving said second ends of said first and second fiberoptics, said tube being at least partially soluble in said particularfluid.
 10. The sensor of claim 8, wherein said member is a solid mass ofsaid material at least partially soluble in said particular fluid. 11.The sensor of claim 1, wherein said means for moving comprises a tubefor receiving said second ends of said fibers from opposite ends thereofand for maintaining said second ends in axial alignment to establishsaid efficient light-transmitting relationship therebetween in theabsence of said particular fluid, and wherein said tube is formed of amaterial that swells upon exposure to said particular fluid, movingsecond ends of said fibers away from one another, and effectivelydestroying said efficient light-transmitting relationship therebetween.12. The sensor of claim 1, wherein said means for moving is encapsulatedin a material soluble in said particular fluid.
 13. The sensor of claim1, wherein the first ends of said fiber optics extend through boresextending axially through a plug adapted to be threaded into a threadedhole extending into a space wherein the presence of said particularfluid is to be monitored, whereby said second ends of said fiber opticsmay be conveniently disposed in said space.
 14. A sensor for detectingthe presence of a particular fluid, comprising:a first fiber optichaving a first end adapted to be juxtaposed to a source of illumination,and a second end adapted to be juxtaposed to a detector of illumination;and cutter means to cut said fiber optic responsive to exposure to saidparticular fluid, wherein said cutter means comprises a releasablylatched cutter biased to cut said fiber optic and a latch normallypreventing said cutting, said latch being of a material deteriorating inthe presence of said particular fluid.
 15. The sensor of claim 14,wherein the material of said latch is a rubber material and saidparticular fluid is a hydrocarbon.
 16. The sensor of claim 14, whereinsaid cutter means comprises a pair of cutting jaws forced together tocut said fiber optic by expansion of a mass of material disposed betweenpincer arms pivoted with respect to one another and supporting saidcutting jaws, said mass of material expanding in response to exposure tosaid particular fluid.
 17. A method of detecting a leak of a particularfluid from a vessel into a space, comprising the steps of:disposing acontinuous fiber optic in said space, said fiber optic having a firstend adapted to be juxtaposed to a source of illumination and a secondend adapted to be juxtaposed to a detector of illumination; disposingone or more cutters adapted to cut said fiber optic in response toexposure to said particular fluid in operative relation to said fiberoptic; and periodically monitoring the light-transmissivecharacteristics of said fiber optic, to determine whether said fiberoptic has been cut by one or more of said cutters responsive to exposureof said one or more of said cutters to said fluid.
 18. The method ofclaim 17, wherein each of said one or more cutters comprises a latchelement of a material having a characteristic affected upon exposure ofsaid element to said particular fluid, whereupon said cutter isactivated to cut said fiber optic.
 19. The method of claim 18, whereinsaid material of said latch element swells upon exposure to said fluid.20. The method of claim 18, wherein said material of said latch elementloses tensile strength upon exposure to said fluid.
 21. A method ofdetecting the presence of a particular fluid in a space, comprising thesteps of disposing second ends of first and second fiber optics in saidspace, said first fiber optic having a first end adapted to bejuxtaposed to a light source, and said second fiber optic having a firstend adapted to be juxtaposed to a light detector;maintaining said secondends of said first and second fiber optics in axially-alignedlight-transmitting relation to one another in absence of said particularfluid; providing bias means for altering said axially-alignedlight-transmitting relation responsive to exposure of said means foraltering said fluid; providing means for maintaining said second ends ofsaid first and second fiber optics in said axially-alignedlight-transmitting relation in absence of said particular fluid; andperiodically monitoring the efficiency of transmission of light betweensaid first and second fiber optics, to determine whether said means foraltering has been exposed to said fluid.
 22. The method of claim 21,wherein said means for maintaining comprises an element of a materiallosing tensile strength upon exposure to said fluid.
 23. The method ofclaim 21, wherein said means for altering said axially-alignedlight-transmitting relation comprises an element of a material swellingupon exposure to said fluid.
 24. The method of claim 23, wherein saidmaterial of said element returns substantially to its originalconfiguration upon cessation of its exposure to said fluid.